A wide variety of devices are used inside and outside hospitals for monitoring patient vital signs. One commonly used device is the Holter monitor which records heart rate, heartbeats, or rhythm continuously during a 24-hour period. The primary purpose of a Holter monitor is to record a patient's heart rate and rhythm during various activities over a long period. The Holter monitor is most helpful when symptoms are frequent. It is also helpful for showing changes in heart rate or rhythm that a patient may not notice.
The Holter monitor is a small data recorder/transmitter connected by wires to several patches containing electrodes. These patches are put on the patient's chest. The tape recorder is placed in a small protective box that fits into a case with straps so it could be easily carried on the shoulder or waist. The electrical representation of the heartbeats travels through the electrodes and wires and is continuously recorded, usually for a 24-hour period. After the recording is completed, the monitor and electrodes can be removed. The recorded data may be transferred to paper for review or reviewed by a technician using a computer.
Another device for monitoring patient vital signs is an event monitor. An event monitor is typically used to record heart rate and rhythms for brief periods; it works only when a person turns on the device. A doctor may recommend an event monitor when symptoms are infrequent, for example, once per week or less.
Event monitors are small, portable devices carried in a purse or attached to a belt or shoulder strap in a manner similar to that of a portable tape/digital player. When symptoms are infrequent, an event monitor may be carried for several days or a few weeks. Most monitors are designed to record the heart rate and rhythm only when a button or switch is turned on. For example, when a symptom occurs, the patient or another person could turn on the event recorder. The event recorder would then record the heart rate and rhythm. The recorded heart rate and rhythm could then be sent by telephone to a recipient in a hospital or clinic for review by a physician.
Another device, the transtelephonic monitor, is similar to an event monitor but differs in that it sends an EKG signal to a recorder by telephone. The primary purpose of both the event and transtelephonic monitors is to record the patient's heart rate and rhythm during a symptom or “event.”
Both Holter and event monitors have several significant deficiencies. First, these devices are wired and require wires running between the device and the recorder, resulting in signal artifact problems. Second, the wires could be uncomfortable to the patient. Third, water could damage the recorder, so the patient cannot swim or bathe while wearing the recorder. Fourth, the monitors do not transmit a “live” signal and are not capable of two-way communication. Thus, emergency personnel cannot use the device to locate a patient requiring emergency care, in case the patient has a heart attack, for example.
Some known wireless devices employ a sensor connected by thin cables to a centralized unit which then wirelessly communicates data to a receiver station. While such devices improve patient mobility, devices that use analog cables still suffer from the same signal artifact problems of the Holter and event monitors. While finger-mounted oxygen sensors, such as oximeters, have been developed that wirelessly communicate data, these devices are bulky, power intensive, and do not detect electrical signals.
Thus, there exists a need for a compact wireless medical sensor that could a deliver performance superior to the above mentioned wired and wireless devices.